While completely spherical implants have long been used by surgeons for replacing lost volume following eye removal, the shape of the front, convex surface that is presented through the covering tissues acts like a ball and socket joint with the related concave posterior surface of the artificial eye. Therefore, slippage is allowed between the eye socket tissues covering the spherical implant and the posterior spherically concave surface of the prosthetic eye. Obviously, a person who has lost an eye desires the best cosmetic replacement, including the best possible correlation of movement with the remaining living eye. To that end, what has been called the "Iowa Implant" was developed and is disclosed in U.S. Pat. No. 3,070,808 issued Jan. 1, 1963 to Edwin Lee Allen for his invention entitled "Eyeball Replacement Buried Muscle Cone Motility Implant Body with Post-Surgical Conformer Prosthesis". The Iowa Implant resulted in a reduction in the number of cases exhibiting droop in the lower and upper eyelids due to support of the prosthesis on the mounds of the implant, and because the prosthesis is keyed to the implant rather than being free to slip, torsional end-point movement was likewise reduced.
In the hands of surgeons who see the merits of the Iowa Implant, it has proven successful in all respects in almost all cases. However, the majority of eye surgeons mistakenly believe the prominent mounds of the implant will very often erode through the covering tissues and result in extrusion. This belief, along with the time consuming surgical techniques required of implantation have been the major criticisms of quasi-integrated implants such as the Iowa Implant. As a result, the spherical (or ball) implant has become the implant of choice of most surgeons.
Therefore, there is a need for an improved implant that will assure successful retention, remove the concerns of possible extrusion and make the surgical procedur e for implantation shorter and more simple. Any such improved implant should also result in a more natural appearance without sacrificing motility.